5b^2-7b=90

Solution for 5b^2-7b=90 equation:

5b^2-7b=90

We move all terms to the left:

5b^2-7b-(90)=0

a = 5; b = -7; c = -90;
Δ = b2-4ac
Δ = -72-4·5·(-90)
Δ = 1849
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1849}=43$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-43}{2*5}=\frac{-36}{10}
=-3+3/5
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+43}{2*5}=\frac{50}{10}
=5
$